Project Summary The uncorrected refractive error is the most common cause of impaired vision throughout the world. The cornea and the lens, the main refractive elements of the eye, work in tandem to focus the incoming light on the retina; refractive errors occur when either the cornea or the lens fails to function properly. It is estimated that refractive errors affect about 150 million Americans who spend over $15 billion each year on eyewear. According to National Health and Nutrition Examination Survey results, over one hundred and ten million Americans could achieve normal vision with refractive correction. Corneal ectasia may happen after refractive surgical procedures such as LASIK and PRK. In addition to corneal ectasia after LASIK, progressive keratoconus affects one in every 2000 Americans and is still an indication for corneal transplant. The progressive nature of this disease significantly affects the mental health and quality of life of patients. In other words, the public health impact of keratoconus is disproportionate to its relatively low prevalence because it primarily affects very young adults. Corneal cross-linking (CXL) treatment is a relatively safe and efficient method to slow down or completely arrest the progression of keratoconus. It has also been used to stabilize and even improve the visual acuity in patients prone to develop ectasia after LASIK. Nevertheless, even after years of research, precise mechanisms underlying this treatment procedure are not fully understood. Keratoconus is associated with the disruption of the collagen fibrils, decreased proteoglycan content, and a significant reduction in corneal biomechanical strength. A clear understanding of the mechanisms that confer elasticity to corneal extracellular matrix provides the necessary information for improvement of the standard CXL procedure and even development of new therapeutic intervention in the diseased states. In this R21-level research study, the PI proposes to investigate the interrelation between CXL therapy and ultrastructure of corneal extracellular matrix. This project characterizes the structural roles of the collagen fibrils, glycosaminoglycans, and collagen fibril? glycosaminoglycan interactions. To this end, the changes in mechanical response of corneal samples following glycosaminoglycan degradation and corneal cross-linking will be measured. The proposed research is innovative because it will devise a novel and unique framework for rigorous investigation of the stiffening effects of the corneal cross-linking therapy. After completing this R21 study and quantifying possible structural roles of collagen fibrils microstructure and glycosaminoglycan composition in effectiveness of the CXL treatment, we will pursue R01 level funding in order to extend our research program and further investigate the biomechanics of corneal tissue in injury and disease.